The present invention relates to golf balls and, in particular, to golf balls having a cover of at least two layers, wherein the inner cover layer material includes an ionomeric material, and the outer cover layer includes a blend of at least one grafted metallocene-catalyzed polymer and at least one ionomer resin neutralized with a metal cation. The outer cover layer blend may optionally include a non-grafted metallocene-catalyzed polymer. The golf balls of the present invention can provide low driver spin and high short iron and partial shot spin.
Golf ball manufacturers are constantly attempting to construct golf balls having a desirable combination of good xe2x80x9cfeel,xe2x80x9d distance, and durability. One way in which the properties of a golf ball may be adjusted is through the cover composition and construction of the ball. Traditionally, softer feeling golf balls were obtained by providing an outer cover formed with natural or synthetic balata over a liquid center surrounded by a tensioned elastomeric wound layer. Because of its softness, however, balata is susceptible to cuts or other damage to the cover, and, thus, lacks the durability required to withstand the numerous mis-hits produced by the average golfer.
For this reason, amateur golfers typically prefer a golf ball constructed with a harder, more durable cover material, such as an ionomer or ionomer blend. Covers formed of ionomeric materials generally provide a good combination of distance and durability. Because of the hard ionomer cover, these balls are difficult to cut, but have a very hard xe2x80x9cfeelxe2x80x9d, and a lower spin rate, making these balls more difficult to draw or fade. The differences in the spin rate can be attributed to the differences in the composition and construction of both the cover and the core.
Many attempts have been made, therefore, to produce a golf ball with the control and feel of a balata-covered ball and the durability of an ionomer-covered ball. For example, U.S. Pat. No. 4,274,637 discloses two- and three-piece golf balls having covers completely or partially formed from a cellular polymeric material to improve backspin.
U.S. Pat. No. 5,002,281 discloses a three-piece solid golf ball having an ionomer cover and a solid core consisting of a soft inner core and a hard outer shell, where the difference in the hardness of the two parts of the core is at least 10 on the JIS-C scale.
Similarly, U.S. Pat. No. 4,781,383 discloses a solid, three-piece golf ball, having an ionomer cover and a core with inner and outer layers, where the inner layer has a diameter of 24 to 29 mm and a Shore D hardness of 15 to 30, and the outer layer has a diameter of 36 to 41 and a Shore D hardness of 55 to 65. The percentage of the ball surface which contacts the club face when the ball is struck is 27 to 35 percent.
European Patent Application No. 0 633 043 discloses a solid, three-piece golf ball with an ionomer or balata cover, a center core, and an intermediate layer. The center core has a diameter of at least 29 mm and a specific gravity of less than 1.4. The intermediate layer has a thickness of at least 1 mm, a specific gravity of less than 1.2, and a hardness of at least 85 on the JIS-C scale.
U.S. Pat. No. 5,586,950 discloses a golf ball having a core and a cover for covering the core, the cover comprising two ionomeric layers of an inner layer, with a high stiffness modulus of approximately 3,000 kgf/cm2 (42,000 psi) to 5,500 kgf/cm2 (78,000 psi) and a thickness of 0.5 to 2.5 mm, and an outer layer with a lower stiffness modulus of approximately 1,000 kgf/cm2 (14,000 psi) to 2,500 kgf/cm2 (35,000 psi) and a thickness of 0.5 to 2.5 mm. The base resin of the inner and outer cover layer contains an ionomer neutralized with a zinc ion.
U.S. Pat. No. 5,803,831 discloses a multi-layer golf ball having soft outer cover, preferably having a Shore D hardness of 48 or less, and a thermoplastic inner cover layer, preferably having a Shore D hardness of at least 65. The outer cover preferably includes at least 75 percent of a soft ionomeric neutralized copolymer formed from a polyolefin, an unsaturated carboxylic acid, and a monomer of the acrylate ester class.
U.S. Pat. Nos. 5,984,806 and 6,015,356 are directed to multi-layer golf balls with smaller and lighter cores produced by including metal particles, or other heavy weight filler materials, in the cover compositions. The covers may include an inner layer that includes a material having a flexural modulus of at least about 15,000 psi and a hardness of at least about 60 Shore D and an outer layer that includes a material, such as a blend of high and low ionomers, having a flexural modulus of from about 1,000 to 10,000 psi and a Shore D hardness of about 65 or less.
U.S. Pat. Nos. 5,553,852 and 5,782,707 disclose a three-piece solid golf ball having a center core, an intermediate layer, and a cover. The ionomeric resin intermediate layer can include various fillers. The outer cover layer, preferably a thermoplastic resin base composition, is softer than the intermediate layer. Iron shots and partial swing shots are affected by this cover design.
U.S. Pat. No. 5,919,101 discloses a solid golf ball comprising a core and a cover formed on the core, wherein the cover has a two-layer structure consisting of an inner cover having a flexural modulus of approximately 3,000 kgf/cm2 (42,000 psi) to 7,000 kgf/cm2 (99,000 psi) and an outer cover formed on the inner cover having a flexural modulus of approximately 1,000 kgf/cm2 (14,000 psi) to 2,800 kgf/cm2 (39,000 psi), and wherein the core is formed from a rubber composition comprising 0.05 to 5 parts by weight of an organic sulfide compound, based on 100 parts by weight of a base rubber. The cover layer can be an ionomer resin, a polyamide, or a nylon.
The above references, however, do not provide an ideal cover material for attaining both good feel and durability. One solution may be golf balls and, in particular, cover layers formed of or blended with metallocene-catalyzed polymers, i.e., polymers produced using single-site metallocene catalysts, which produce polymers with a narrow molecular weight distribution and uniform molecular architecture, so that the order and orientation of the monomers in the polymer, and the amount and type of branching is essentially the same in each polymer chain.
The narrow molecular weight distribution and uniform molecular architecture provides metallocene-catalyzed polymers with properties that are not available with conventional polymers, and allow polymers to be produced having unique properties that are specifically tailored to a particular application. The desired molecular weight distribution and the molecular architecture are obtained by the selection of the appropriate metallocene catalyst and polymerization conditions.
Processes for grafting monomers onto polymers and, in particular, polyolefins, are known in the art. European Patent Application No. 0 266 994 discloses a process for grafting ethylenically unsaturated monomers, such as unsaturated carboxylic acids and anhydrides and derivatives thereof, onto copolymers of ethylene. The disclosed process includes the steps of forming an admixture of the copolymer, monomer, and 25 to 3,000 ppm of an organic peroxide having a half-life of about one minute to 120 minutes at 150xc2x0 C., and mixing the resultant admixture in an extruder at a temperature above the melting point of the copolymer for a period of time at least four times the half-life of the organic peroxide. The resultant grafted copolymer is then extruded into a shaped article.
U.S. Pat. No. 5,106,916 discloses a process for the catalytic grafting of an ethylenically unsaturated monomer onto a copolymer in which the process of EPA 0 266 994 is modified by the addition of a catalyst comprising water and at least one phosphorous-containing compound selected from the group consisting of compounds of formula HPO(ORI)2, phosphite compounds of formula P(OR2)3 and formula (OR3)Pxe2x80x94Oxe2x80x94R4xe2x80x94Oxe2x80x94P(OR5)2, and di-substituted pentaerythritol diphosphites of formula (R6O)Pxe2x80x94O2xe2x80x94RPEO2xe2x80x94P(OR7), where O2RPEO2 is the pentaerythritol moiety, and R1-R7 are specified organic functional groups.
Grafted metallocene-catalyzed polymers, which are commercially available, share the advantages of non-grafted metallocene-catalyzed polymers, including a narrow molecular weight distribution and uniform molecular architecture. The addition of functional groups to the metallocene-catalyzed polymers by grafting allows polymers to be produced having properties that are not available with unfunctionalized metallocene-catalyzed polymers or polymers formed without the use of metallocene catalysts.
While different blend combinations of species of one variety of polymer, such as ionomers, have been successfully used in the prior art, different polymers, such as ionomers and balata or other non-ionic polymers have not been successfully blended for use in golf ball covers. In general, prior art blends of polymer components are immiscible, i.e., heterogeneous on a microscopic scale, and incompatible, i.e., heterogeneous on a macroscopic scale, unless strong interactions are present between the polymer components in the mixture, such as those observed between ionomers and polymers containing carboxylic acid groups. In particular, this lack of compatibility exists when an ionomer is blended with a polyolefin homopolymer, copolymer, or terpolymer that does not contain ionic, acidic, basic, or other polar pendant groups, and is not produced with a metallocene catalyst. These mixtures often have poor tensile strength, impact strength, and the like. Hence, golf balls produced from these incompatible mixtures would be expected to have inferior golf ball properties such as poor durability, cut resistance, and so on. In contrast, a compatible blend may be heterogeneous on a microscopic scale, but is homogeneous on a macroscopic scale, and, thus, has useful golf ball properties.
U.S. Pat. Nos. 5,397,840 and 5,516,847 are directed to golf ball covers comprising a blend of copolymers wherein one or more of the copolymers is a nonionic copolymer, such as a copolymer of ethylene and acrylic acid or methacrylic acid or a copolymer of propylene and acrylic acid, and one or more of the copolymers is an ionic copolymer, such as sodium and zinc neutralized copolymers of ethylene and acrylic acid. However, the xe2x80x9cionic copolymersxe2x80x9d are defined in U.S. Pat. No. 5,397,840 as copolymers of an xcex1-olefin and a metal salt of an xcex1,xcex2-unsaturated carboxylic acid, and the xe2x80x9cnon-ionic copolymersxe2x80x9d are copolymers or terpolymers containing ethylene or propylene and acrylic or methacrylic acid monomers. Therefore, strong interactions exist between the metal salts of the xe2x80x9cionic copolymersxe2x80x9d and the acrylic or methacrylic acid monomers of the xe2x80x9cnon-ionic copolymersxe2x80x9d that allow compatible blends to be formed. These interactions do not exist in prior art blends of ionomers and polymers that are truly non-ionic or nonpolar, in particular, those polymers produced with a process that does not involve the use of a metallocene catalyst.
U.S. Pat. Nos. 4,986,545; 5,098,105; 5,187,013; 5,330,837; and 5,338,610 disclose golf balls having covers comprising blends of ionomers and modified thermoplastic elastomers, where the thermoplastic elastomers are conventional polymers, i.e., polymers polymerized using catalysts other than metallocene catalysts. The modified polymers include maleic anhydride modified ethylene-propylene copolymers, maleic anhydride modified styrenic block copolymers, maleic anhydride modified ethylene-vinyl acetate copolymers, brominated styrene-isobutylene copolymers, amine modified ethylene-propylene rubber, and polar modified para-methylstyrene-isobutylene copolymers. However, blends of ionomers with modified polyolefins are not exemplified.
U.S. Pat. Nos. 5,542,677 and 5,591,803 are directed to golf ball cover compositions containing blends of high or low carboxylic acid based copolymers and ethylene copolymers such as ethylene alkyl acrylates.
U.S. Pat. No. 5,321,089 is directed to a golf ball cover composition comprising a blend of ethylene-methyl acrylate, an ionomer resin, and a compatibilizer.
As shown in U.S. Pat. No. 5,703,166, metallocene-catalyzed polymers and ionomers form compatible blends of useful golf ball properties. However, there is no known prior art disclosure of golf balls incorporating compositions comprising grafted metallocene-catalyzed polymers.
U.S. Pat. No. 5,981,658 discloses golf ball compositions that contain non-ionic olefinic copolymers produced by metallocene catalysts functionalized with a post-polymerization reaction. The disclosed compositions exhibit improved mechanical properties, such as tensile strength and flexural modulus. The polymers disclosed in the ""658 Patent do not, however, address problems with processability of these types of polymers.
U.S. Pat. No. 5,830,087 discloses a multi-layer golf ball having a coefficient of restitution of at least about 0.78 with a central core, an inner cover layer containing a non-ionomeric polyolefin material, preferably a plastomer, and an outer cover layer including a thermoplastic material. The golf ball of the invention can be configured having an inner cover layer containing a non-ionomeric material, such as a metallocene-catalyzed polyolefin, and the outer cover layer containing ionomer.
It would be advantageous to provide a golf ball having a cover including at least two layers, wherein the outermost layer includes at least one grafted metallocene-catalyzed polymer, and preferably a blend including a metallocene-catalyzed polymer, to allow improved play characteristics with all types of clubs (i.e., high spin with irons and partial shots and low spin off the driver). The present invention provides such a cover.
The present invention is directed to a golf ball including a core and a cover, wherein at least one of the cover or the core is formed from a polymer blend including at least one grafted metallocene-catalyzed polymer, at least one ionomer, and at least one non-ionomer.
In one embodiment, the golf ball includes a cover having at least one of a dimple coverage of about 60 percent or greater, a hardness from about 35 to 80 Shore D, or a flexural modulus of about 500 psi or greater, and wherein the golf ball has at least one of a compression from about 50 to 120 or a coefficient of restitution of about 0.7 or greater.
In a preferred embodiment, the grafted metallocene-catalyzed polymer has a flexural modulus of from about 500 psi to 100,000 psi, the ionomer has a flexural modulus of from about 1,000 psi to 200,000 psi, and the non-ionomer has a flexural modulus of from about 500 psi to 100,000 psi. In one embodiment, the cover includes the polymer blend. In another embodiment, the cover layer material has a Shore D hardness of about 75 or less. In another embodiment, the cover layer has a thickness of from about 0.015 inches to 0.125 inches. In still another embodiment, the grafted metallocene-catalyzed polymer has been functionalized by grafting an ethylenically-unsaturated monomer onto the at least one metallocene-catalyzed polymer using a post-polymerization reaction. Preferably, the ethylenically-unsaturated monomer is an olefinic monomer having a functional group selected from the group consisting of sulfonic acid, sulfonic acid derivatives, chlorosulfonic acid, vinyl ethers, vinyl esters, primary amines, secondary amines, tertiary amines, mono-carboxylic acids, dicarboxylic acids, partially or fully ester derivatized mono-carboxylic acids, partially or fully ester derivatized dicarboxylic acids, anhydrides of dicarboxylic acids, cyclic imides of dicarboxylic acids, and ionomeric derivatives thereof, and combinations thereof. More preferably, the ethylenically-unsaturated monomer includes maleic anhydride.
In another embodiment, the at least one grafted metallocene-catalyzed polymer is present in an amount of from about 5 to 50 phr. Preferably, the at least one grafted metallocene-catalyzed polymer is present in an amount of from about 5 to 30 phr. In still another embodiment, the at least one ionomer is present in an amount of from about 95 to 50 phr. In a preferred embodiment, the at least one ionomer is present in an amount of from about 95 to 70 phr. In an alternative embodiment, the at least one non-ionomer is present in an amount of from about 1 to 25 phr. Preferably, the at least one non-ionomer is present in an amount of from about 5 to 20 phr.
In one embodiment, the core includes the polymer blend of the present invention. In an alternative embodiment, the core includes a center and at least one intermediate layer disposed between the center and the cover. The at least one intermediate layer may include the polymer blend while the cover includes a thermoset or thermoplastic material. Additionally, the cover may include the polymer blend and a thermoplastic material. The thermoplastic material may include at least one ionomer. Preferred thermoset materials, if used, include polyureas, polyurethanes, and mixtures thereof.
In yet another embodiment, at least one of the core, cover, or intermediate layer includes a density-adjusting filler. The density-adjusting filler preferably includes zinc oxide, barium sulfate, silica, calcium carbonate, zinc carbonate, tungsten, titanium, and mixtures thereof. In another embodiment, the at least one intermediate layer includes the polymer blend of the present invention. In one embodiment, the center is fluid-filled and, alternatively, in another embodiment, the center is a solid or hollow center. In still another embodiment, the at least one intermediate layer includes a tensioned elastomeric thread disposed about a fluid-filled center or a solid center.
In one embodiment, the grafted metallocene-catalyzed polymer is formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer selected from the group consisting of polyethylene and copolymers of ethylene with propylene, butene, pentene, hexene, heptene, octene, and norbornene. In another embodiment, the grafted metallocene-catalyzed polymer is formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer selected from the group consisting of polyethylene and copolymers of ethylene with butene. In a preferred embodiment, the grafted metallocene-catalyzed polymer is formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer of the formula: 
wherein R1 is hydrogen; R2 is hydrogen or lower alkyl selected from the group consisting of CH3, C2H5, C3H7, C4H9, and C5H11; R3 is hydrogen or lower alkyl selected from the group consisting of CH3, C2H5, C3H7, C4H9, and C5H11; R4 is selected from the group consisting of H, CH3, C2H5, C3H7, C4H9, C5H11, C6H13, C7H15, C8H17, C9H19, C10H21, and phenyl, in which from 1 to 5H and R4 can be replaced by substituents selected from the group consisting of COOH, SO3H, NH2, F, Cl, Br, I, OH, SH, silicone, lower alkyl esters and lower alkyl ethers, with the proviso that R3 and R4 can be combined to form a bicyclic ring; R5 is hydrogen, lower alkyl including C1-C5, carbocyclic, aromatic or heterocyclic; R6 is hydrogen, lower alkyl including C1-C5, carbocyclic, aromatic or heterocyclic; and wherein x ranges from 99 to 50 weight percent of the polymer, y ranges from 1 to 50 weight percent of the polymer and z ranges from 0 to 49 weight percent of the polymer.
In one embodiment, the polymer blend has a foamed structure. In another embodiment, the non-ionomeric polymer has the chemical structure: 
wherein x=50 to 99 weight %; y=1 to 50 weight %; z=0 to 49 weight %; R1xe2x95x90H or CH3; R2=methyl, ethyl, propyl, butyl, pentyl, hexyl, hectyl, octyl, or isobornyl; and n=0 to 12. In yet another embodiment, the non-ionomer includes an olefinic homopolymer, an olefinic copolymer, an olefinic terpolymer, and mixtures thereof. Preferably, the non-ionomer is an acid-containing ethylene copolymer including ethylene/methacrylic acid, ethylene/acrylic acid, and mixtures thereof. In another embodiment, the non-ionomer is an acid-containing ethylene terpolymer including ethylene/acrylic acid/n- or isobutyl acrylate, ethylene/methacrylic acid/n- or isobutyl acrylate, ethylene/acrylic acid/methyl acrylate, ethylene/methacrylic acid/methyl acrylate, ethylene/acrylic acid/isobornyl acrylate or methacrylate, ethylene/methacrylic acid/isobornyl acrylate or methacrylate, and mixtures thereof. It is preferred that the non-ionomer is present in an amount from about 1 phr to 25 phr of the total polymer. In an alternative embodiment, the polymer blend further includes a non-grafted metallocene-catalyzed copolymer. Preferably, the non-grafted metallocene-catalyzed copolymer includes polyolefin plastomers, polyolefin elastomers, or a mixture thereof.
The present invention is also directed to a golf ball including a core having a center, a cover, and at least one intermediate layer disposed between the core and the cover, wherein at least one of the cover, the center, and the at least one intermediate layer is formed from a polymer blend including from about 5 to 50 phr of at least one grafted metallocene-catalyzed polymer, from about 95 to 50 phr of at least one ionomer, and from about 1 to 25 phr of at least one non-ionomer.
The present invention is also directed to a golf ball including a core having a center, a cover, and at least one intermediate layer disposed between the core and the cover, wherein at least one of the cover, the center, and the at least one intermediate layer is formed from a polymer blend including from about 5 to 50 phr of at least one grafted metallocene-catalyzed polymer formed by grafting an ethylenically-unsaturated monomer onto a metallocene-catalyzed polymer selected from the group consisting of polyethylene and copolymers of ethylene and butene; from about 95 to 50 phr of at least two ionomers, each including an ethylene methacrylic/acrylic acid copolymer wherein at least one ionomer is partially neutralized with lithium and at least one ionomer is partially neutralized with sodium; and from about 1 to 25 phr of at least one non-ionomer of the chemical structure: 
wherein x=50 to 99%; y=1 to 50%;z=0 to 49%; R1xe2x95x90H or CH3; R2=methyl, ethyl, propyl, butyl, pentyl, hexyl, hectyl, octyl, and isobornyl; and n=0 to 12.
The present invention is also directed to a golf ball including a core, an inner cover having at least one layer including a material having a first Shore D hardness formed over the core and including a thermoplastic material, an outer cover layer including a material having a second Shore D hardness disposed about the inner cover, formed from a polymer blend including at least one grafted metallocene-catalyzed polymer and an ionomer component, wherein the first Shore D hardness is greater than the second Shore D hardness. In one embodiment, an intermediate layer, preferably a tensioned elastomeric layer, is situated between the core and the inner cover layer.
In one embodiment, the polymer blend includes about 30 percent by weight or greater of the at least one grafted metallocene-catalyzed polymer. In another embodiment, the polymer blend includes about 35 percent by weight or greater of the at least one grafted metallocene-catalyzed polymer.
In one embodiment, the thermoplastic material of the inner cover layer includes at least one ionomer resin. Preferably, the ionomer resin is neutralized with a metal cation including at least one of Na, Li, Ca, K, or Mg.
In another embodiment, the ionomer component of the outer cover layer blend includes at least two ionomer resins, each neutralized with a different metal cation selected from the group consisting of Zn, Na, Li, Ca, K, and Mg.
In one embodiment, the inner cover layer has a thickness of about 0.039 inches or less, preferably from about 0.02 inches to 0.038 inches.
In another embodiment, the first Shore D hardness is about 60 or greater and the second Shore D hardness is about 60 or less. In yet another embodiment, the first Shore D hardness is from about 65 to 80, and the second Shore D hardness is from about 45 to 60. In still another embodiment, the first Shore D hardness is from about 65 to 80, and the second Shore D hardness is from about 51 to 60.
In one embodiment, the outer cover layer material has a flexural modulus of about 10,000 psi or greater. In another embodiment, the outer cover layer has a thickness from about 0.01 inches to 0.1 inches, preferably from about 0.02 inches to 0.06 inches. In yet another embodiment, the golf ball has at least one of a compression of about 80 or less and a coefficient of restitution of about 0.8 or greater, or both.
In one embodiment, the core includes polybutadiene having an uncrosslinked Mooney viscosity of about 40 or greater. In another embodiment, the core is substantially free of organic sulfides. In yet another embodiment, the core further includes at least one inorganic sulfide.
The core preferably has an outer diameter of about 1.51 inches or greater and a compression of about 90 or less, more preferably from about 65 to 90.
The present invention is also directed to a method of making a golf ball, including the steps of providing a golf ball, forming an inner cover having at least one layer, including a material having a Shore D hardness of about 60 or greater, and wherein the inner cover includes at least one ionomer resin and is substantially free of metallocene-catalyzed polymer, and forming an outer cover having at least one layer, including a polymer blend having a Shore D hardness of about 60 or less disposed about the inner cover, wherein the polymer blend includes at least one grafted metallocene-catalyzed polymer and at least one ionomer resin.